1. Gas Welding
Chapter 5

2. Oxyacetylene Welding Definition:
Join metal by heating surfaces to be joined to melting point with gas flame
Fusing metal into homogeneous mass
Letting it solidify into a single unit
Flame in cone reaches temperatures as high as 5800º to 6300ºF
Filler rod may or may not be used to intermix with molten pool

3. Oxyacetylene Process
During first part of this century used as major welding process both for fabrication and construction, maintenance and repair
Today use limited for industrial production purposes
Still used for brazing, soldering, welding metals with low melting points; general maintenance and repair work

4. History of Oxyacetylene Welding
Early Egyptians, Greeks, and Romans used alcohol or oil flame to fuse metals
In nineteenth century various gases tested
In 1847, Robert Hare fused platinum with oxyhydrogen flame
In 1880, production of oxygen and hydrogen through electrolysis of water made distribution of gases in cylinders under pressure
Late 1800s experiments done with oxygen-coal gas and air-hydrogen flames

5. Discoveries Leading to the Oxyacetylene Process
In 1836, Edmund Davey discovered acetylene gas
In 1862, acetylene gas produced from calcium carbide
In 1895, Thomas L. Willson produced calcium carbide commercially
Used for residential lighting
In 1895, LeChatelier discovered that combustion of acetylene with oxygen produced flame hotter than any other gas flame

6. Discoveries Leading to the Oxyacetylene Process
In 1900, Edmond Fouche invented high pressure acetylene torch
Later designed low pressure torch (worked on injector principle)
In 1906 Eugene Bourbonville brought first welding torch to this country
Process first used for maintenance and repair
During World War I oxyacetylene welding became production tool

7. Gases Oxyacetylene welding process uses two principal gases
Oxygen and acetylene
Other gases can be used for cutting and heating
Propane
Natural gas
Mapp® gas\

8. Various Fuel Gas Efficiencies
Normal
Btus Usable heat Flame Oxygen velocity
Fuel Gas (ft3) (s/ft2) temp. per ft3 of fuel (ft/s)
Acetylene ,700 5,420ºF
Mapp® ,540 5,301ºF
Propane ,500 5,190ºF
Natural gas ,600 5,000ºF
Hydrogen ,500 4,600ºF

9. Various Gas Cylinders
Thermadyne Industries, Inc.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

10. Oxygen Gaseous Chemical element in air
Necessary for life
Most abundant chemical element in crust of Earth
No color, odor, or taste
Does not burn, but supports combustion
Substances that do not burn in air will in oxygen

11. Oxygen Production
Two commercial processes used in production of oxygen
Separation of water into oxygen and hydrogen by electrolysis of water
Separation of air into oxygen and nitrogen by liquefying air

12. Oxygen Distribution Distributed in steel or aluminum cylinders
Used for medical gases (smaller size)
Made of high strength 6061-T6 alloy
Steel cylinders
Made from single plate of high-grade steel
Heat treated to develop maximum strength and hardness
Seamless, drawn-steel vessels with iron neck ring shrunk on at top and cylinder value screwed into neck
High pressure – undergo rigid testing
Distributed in steel or aluminum cylinders
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

13. Valve Mechanisms Must be opened to release oxygen
Double-seated valve perfectly tight when completely open or closed
Valve protected from damage by iron cap that screws on neck ring
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

14. Gas Cylinders
Charged with oxygen at pressure of about 2,200 p.s.I. at 70ºF
Gas temperature
Increase: gas expands and increases pressure
Decrease: gas contracts and reduces pressure
Safety device on cylinder valve to blow off oxygen when excess pressure
Occurs, oxygen lost
DO NOT store where cylinder can be overheated

15. Capacity of Cylinder Three cylinder sizes used for welding and cutting
Gas suppliers fill tanks with varying amounts
Large size: cubic feet of oxygen
Full: 148 to 152 pounds; Empty: pounds
Middle size: cubic feet of oxygen
Full: 89 to 101 pounds; Empty: pounds
Small size: cubic feet of gas
Full: 67 pounds; Empty: 60 pounds

16. Safety Precautions
Take special care to keep oil and grease away from oxygen
When using, do not place cylinders where oil might drop of them from overhead bearings
Never use oxygen in pneumatic tools or to start internal combustion engines
Never use oxygen to blow out pipe or hose lines, dust clothes or create head pressure in tank of any kind

17. Safety Precautions
Do not store oxygen cylinders near acetylene generator, carbide, acetylene, or other fuel-gas cylinders
Do not use cylinder as roller or lift it by cap
Keep cylinders away from welding operation and close cylinder valve when work completed
Keep cylinders away from any electrical contact

18. Acetylene Most widely used of all fuel gages
Both welding and cutting
Generated as result of chemical reaction that takes place when calcium carbide comes in contact with water
Tests show oxyacetylene flame temperatures up to approximately 6,300ºF
Very rapid rate of preheating
Burns with smoky flame, gives off carbon, has peculiar odor

19. Characteristics of an Effective Welding Fuel Gas
High flame temperature
High rate of flame propagation
Adequate heat content
Minimum chemical reaction of flame with base and filler metal
Acetylene most closely matches all these requirements and used for welding purposes.

20. Acetylene Production and Distribution
Commercial acetylene made from calcium carbide – referred to as carbide
Gray, stonelike substance
Product of smelting coke and lime in electric furnace
Several sizes available
Distributed in standard steel drums
100 pounds for use in acetylene generators

21. Acetylene Cylinders Constructed differently from oxygen cylinders
Free acetylene should not be stored at pressure above 15 p.s.i.
Safety solved by packing cylinders with porous material saturated with acetone
Acetone – liquid chemical having property of dissolving or absorbing many times the volume of acetylene
Strong steel container (packed completely full)
Handle with care

22. Three Basic Acetylene Cylinders
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

23. Valve Mechanisms Acetylene drawn off through valve
Some cylinders valve located in recessed top
Others valve located on convex top
Simpler in construction than oxygen valve
Does not have to stand high pressure
Opened only about 1 ½ turns
Can be turned off quickly in case of fire
Safety fuse plugs also provided

24. Capacity of Cylinder
Full cylinder of acetylene has pressure of about 225 p.s.i.
Two sizes used for welding and cutting
Large size contains 300 cubic feet of acetylene and weighs about 232 pounds when full
Small size contains 100 cubic feet and weighs 91 pounds when full
Two special sizes (10 cubic ft. and 40 cubic ft.)
Not all acetylene in cylinder can be used

25. Safety Precautions Remember acetylene will burn.
It will form explosive mixture with air.
Do not leave acetylene cylinders on their sides
Store valve end up
Store cylinders in well-protected, ventilated, dry location
Away from highly combustible material or sources of heat
Keep valve cap on when not in use

26. Safety Precautions
Use warm (not boiling) water on the valve if it becomes clogged with ice (Never a flame!)
Fusible safety plugs melt at boiling point of water
Handle acetylene cylinders carefully
Damages could cause leakage
Advise supplier immediately if acetylene leaks around valve spindle when valve opened
Close spindle and move cylinder to outside area
Never tamper with fuse plugs

27. Propane Gas Hydrocarbon present in petroleum and natural gas
Used primarily for oxyfuel heating, cutting, soldering and brazing
Sold and transported in steel cylinders containing from 20 to 100 pounds of liquefied gas
Also supplied by tank car and bulk delivery
Oxypropane flame temp less than oxyacetylene
Takes longer to bring steel to melting point
Used for soldering and alloy brazing

28. Mapp® Gas Liquefied acetylene compound
Fuel gas for oxyfuel heating and cutting
Strong smell (aid in discovering leaks)
Mixed with oxygen, flame is 5,301ºF
Heating and cutting somewhat slower
Lower temperature
Overall expenses lower due to reduced handling costs and lower gas costs

29. Mapp® Gas Use as fuel gas for heating and cutting is growing
Distributed in bulk or steel-cylinders
Shutoff valve similar to ones on acetylene cylinder
Liquefied and stabilized so can be used at pressures as high as 375 p.s.I. at 170ºF
Explosive limits lower than acetylene
Can be stored in free state and at high pressures

30. Safety in Handling Mapp® Gas
Forms an explosive mixture with air
Same general precautions used with handling acetylene cylinders should be observed
Safest of industrial fuels
Explosive limits of Mapp® gas vapor in air and oxygen much narrower than acetylene, same as propane and natural gas
Can smell it at concentrations as low as 0.01 percent

31. Manifold Distribution
Supplies both oxygen and fuel gas to number of work stations
Acetylene manifolds must be equipped with flash arrester to prevent flashback through manifold into cylinders
Each cylinder connected to manifold by means of an individual pigtail flash arrester and backcheck valves

32. A typical station outlet for both oxygen and acetylene pipelines from the source.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

33. Thermadyne Industries, Inc.
Manifold Regulator
Reduces pressure to 50 or 75 pounds in line that goes to station outlets in shop
Full pressure of 2,000 p.s.i. in oxygen manifold pipes
Work station also equipped with acetylene and oxygen regulator for further pressure control
Thermadyne Industries, Inc.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

34. Acetylene Generators Two general types
Calcium carbide dropped into water
Water allowed to drip on carbide
Carbide-to-water generators used to produce acetylene gas for welding and cutting
Water absorbs heat given off by chemical reaction
Gas purified by bubbling through water

35. Acetylene Generator
Rexarc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

36. Acetylene Generators Two classes of generators
Low pressure (less than 1 p.s.i.)
Medium pressure (1 to 15 p.s.i.)
Generating capacities range from
30 cu feet of acetylene per hour for small portable
6,000 cu feet acetylene per hour for medium-pressure generator

37. Acetylene Generator Further classified as stationary or portable
Example of portable acetylene generator
Rexarc
Further classified as stationary or portable
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

38. Protective Equipment
Functions may be combined in one device or provided by separate devices
Located in main supply line, head of each branch line in manifold system or at each location where fuel gas withdrawn
Backflow protection should be provided to prevent fuel gases from flowing into oxygen system
Flashback protection should be provided to prevent flame from passing into fuel-gas system

39. Oxyhydrogen Welding (OHW)
Form of gas welding once used extensively
Today have limited use
Flame produced by burning two volumes of hydrogen with one volume of oxygen
Temperature of ~ 4,100ºF
Almost invisible
Similar equipment to that used for oxyacetylene welding
Need regulator specifically designed for hydrogen

40. Oxyhydrogen Welding (OHW)
Relatively low flame temperature
Used principally in welding metals with low melting points
Used extensively in welding of lead
Thicknesses of lead up to 1/4 or 3/8 inch
No deposit of carbon

41. Flash Arrestors Generally make of sintered metal alloy
Prevents flame from moving upstream of arrestor
Does not protect torch or tip
Neither does check valve
Best way to assure that accidents don’t happen is to follow all safety operating procedures.

42. Internal View of a Check Valve
Prevents the Reverse Flow of Gases
Thermadyne Industries, Inc./Victor Equipment Company
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

43. Internal View of a Flashback Arrestor
Thermadyne Industries, Inc./Victor Equipment Company
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.